Studies indicate obesity doubles a woman's chances of having a baby with neural tube defects, and even adequate folic acid intake does not fully protect against the increase in risk.

Compared with normal-weight women, obese women have a greater risk of developing complications during pregnancy. Their babies are also more likely to be admitted to neonatal intensive care units.

In a report published today, the public affairs committee of the Teratology Society officially declared obesity a pregnancy risk factor, adding that women should be told about the risk in the same way that they are warned about the dangers of smoking and drinking alcohol during pregnancy. The Teratology Society studies the causes and processes of birth defects to improve diagnosis and prevention.

"Just as clinicians have been encouraged to counsel women who are pregnant or may become pregnant about folic acid, smoking cessation, and avoidance of [alcohol], [we] recommend that clinicians counsel women about appropriate caloric intake and exercise," the report noted.

Women who are obese are more likely than women who aren't to require cesarean sections.

A study from France found that hospital costs for prenatal care were dramatically higher for overweight and obese women. Costs were fivefold to 16-fold greater than for normal-weight women, depending on how much extra weight the women carried.

The committee recommended that obese women should try to lose weight before becoming pregnant. But it warned women not to diet during pregnancy, noting that "adequate nutrition is important for pregnant women and women planning pregnancy."

Some recent reports suggest that women with gastric banding can have normal pregnancies and better pregnancy outcomes than women who do not have the surgery, but the committee concluded that "it appears reasonable to recommend that pregnancy be delayed until surgery-related weight loss has stabilized."

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Docs Should Talk About Weight

The report noted that the link between maternal obesity and neural tube defects has been confirmed in numerous studies. Neural tube defects are among the most serious and common birth defects in the United States. Each year, an estimated 2,500 babies are born with these defects, and many other affected pregnancies end in miscarriage and stillbirth. The most common neural tube defect is spina bifida, which is a leading cause of childhood paralysis. The research suggests a doubling of risk for babies born to obese women, compared with those born to normal-weight women.

The risk is still very small -- two affected births for every 1,000 among women who are obese instead on one in 1,000. But Scialli says while this is not a huge number, it is not insignificant.

"There are 4 million pregnancies in the U.S. each year, so two in a thousand still ends up being a lot of kids," he says.

And while folic acid supplementation helps protect everyone from the birth defect, obese women who got enough folic acid were still twice as likely as normal-weight women who also got enough to deliver babies with neural tube defects.

Scialli says health care providers must make sure that their patients know about the risks.

"The point is not to bash obese women and make them feel bad," he says. "It is to make health care providers aware of this, because they are in a position to make a difference."

The American College of Obstetricians and Gynecologists (ACOG) put out a similar message last fall, calling on ob-gyns to evaluate all of their patients for obesity and to inform patients of potential pregnancy complications associated with carrying excess weight.

ACOG former President Vivian M. Dickerson, MD, says ob-gyns have an obligation to discuss the dangers of obesity with their patients.

"While the topic may make us uncomfortable, in that we feel we may offend our patients, we should take a more direct approach in helping to identify their health risks," she says.